The Italian press are reporting that Microsoft has uspended the messenger service following a virus attack affecting the USA and the Far East.
The virus is called WORM-BROPIA.F and is linked to an attachment called sexy.jpg which shows the picture of a chicken with a tan (quoting the article - don't know what the link is there!)
Source (in Italian)
Update:
Did a bit more digging around - the virus thing is a few days old - but Microsoft is experiencing problems in a data centre - see
zdnet news item
So if yours ain't working just yet, you know why..